1. Field of the Invention
This invention relates to a distance measuring device and more particularly to a device adapted for measuring a distance to an object by projecting a "distance measuring" light onto the object from the device; by receiving light reflected from the object with a light receiver; by photo-electrically converting the reflected light incident on the light receiver; by detecting the amount of electric charge obtained and stored through the photo-electric conversion; and by determining the object distance according to a resulting detection signal. The invention also relates to a control device arranged to adjust the quantity of light projected from a light source to illuminate the object on the basis of the intensity of the light reflected from the object.
2. Description of the Prior Art
Devices of various kinds have been developed for the purpose of measuring the distance at which an object is located relative to a photographic camera. These distance measuring devices for cameras of the prior art include so-called automatic focusing devices. There light of a predetermined value is projected on a photographic object; the object distance is detected by receiving light reflected from the object with a detector (or a light sensitive element); and the focus point of a photo-taking lens is adjusted by shifting the position of the lens according to a detected distance signal.
Known automatic focusing devices of the prior art are always arranged to project a given fixed quantity of light. Therefore, the quantity of the light reflected by the object is excessive when the object is nearby and is insufficient when the object is far away. This makes it difficult to obtain a good distance signal and the accuracy of the resulting measurements have been unsatisfactory. Also, unimproved conventional distance measuring devices have wasted energy by always projecting a fixed quantity of light during a distance measuring operation.
Various types of light receivers for use in photographic camera distance measuring devices have been developed. These include photosensor devices of the electric charge storing type such as semiconductor CCD photosensors, semiconductor CCD photodiodes, etc. Such a photosensor device is disclosed by U.S. Pat. No. 4,315,159 corresponding to Japanese Laid-Open Patent Application No. SHO 54-154382. The photosensor device of this U.S. patent comprises a photosnesor having at least one sensor element which generates an electric charge according to a light incident thereon; first and second electric charge stores each of which is provided with the same number of electric charge storing the electric charge generated by the sensor element; a first control gate which controls the flow of the electric charge from the photosensor to the first electric charge store; and a second control gate which controls the flow of the electric charge from the photosensor to the second electric charge store. The device is thus arranged to apply voltages alternately to the first and second gates to allow the first and second electric charge stores to alternately store the electric charge generated at the photosensor part. In a photosensor device such as the one disclosed by this U.S. patent, it is sometimes not possible to obtain a correct signal representing the extent to which a focusing lens is to be shifted. This occurs where the detected value of the electric charge stored at the electric charge store varies as the reflection factor, or location of the object varies to produce stronger or weaker light reflections from the object.